A cold adapted influenza A reassortant virus vaccine was shown to be poorly immunogenic at a dose of 106TCID50 in infants less than six months of age, whereas it was highly immunogenic in slightly older children. These results indicate that young age decreases the response to the hemagglutinin of the influenza A virus and suggest that higher doses of vaccine and a multi-dose schedule of immunization will be required for successful immunization in this age group. Such studies are in progress. The bovine parainfluenza virus type 3 (BPIV3) vaccine was found to be satisfactorily attenuated, stable genetically, poorly transmissible, and immunogenic in seronegative infants and young children. Studies of this promising candidate in the target population of the very young seronegative infant and in older seronegative infants and children are in progress. The cp45 human PIV3 vaccine also was found to be safe, satisfactorily infectious, genetically stable, and immunogenic in seronegative infants and children. A CRADA is being developed to accelerate evaluation of this promising candidate vaccine strain. Live attenuated respiratory syncytial virus (RSV) vaccine candidates are currently being evaluated in Phase 1 trials in infants and young children. One subgroup A virus vaccine that contains both host-range and ts mutations, namely RSV A2 cpts-248/955, is infectious in young seropositive vaccinees and, importantly, the ts phenotype of the virus shed is stable. This vaccine is currently being studied in seronegative infants and children. The evaluation of three to four other candidate subgroup A and B vaccine candidates will begin this coming year.